Testing of integrated circuit (IC) devices is an essential part of IC device production. For analog or linear products, voltage drop and current flow are two important parameters that need to be determined in the testing of such products. These two parameters are highly affected by the arrangement of the test circuitry, and the quality of the contact points within the tester. For testing systems that use contact fingers, a set of two contact fingers clamping the IC device leads from the top and bottom allows four-terminal circuit for testing. One pair of contact fingers provides the contact for passing the measurement current, while the other contact finger provides the contacts for measuring the voltage drop at the device under test. This allows the testing system to measure any voltage drift or drop due to resistance within the test lead or due to contact resistance, and adjust the voltage accordingly to provide a constant preset voltage for testing to be performed.
Although contact finger sets provide a four terminal circuit, recent trends have been to shift from testing by contact fingers to testing by test sockets. One important reason is that for each type of IC packaging, a different set of contact fingers have to be manufactured. Adapatition from standard sets is not possible. On the other hand, test sockets have the advantage that they can be adapted by the IC manufacturer to be used for testing their IC packages. Therefore, a wide range of standard sockets can be supplied for testing numerous types of IC devices.
There is, however, no test socket in the market that is provided with Kelvin contacts to allow four-terminal measurements. The main difficult is that this feature requires two pairs of contact points for each pair of corresponding leads of the IC device to be tested. In the case of contact finger sets, the two fingers in each pair contact the IC device lead bi-directionally. Therefore, both the top and bottom surface of the lead is utilized, and there is sufficient room for contact to be made effectively. In the case of a contact socket, however, the testing finger contacts the IC device lead in only one direction from the socket side. Due to the short length of the tip and the small diameter of the IC device lead, conventional thinking has been that it is not feasible to provide a Kelvin contact for testing sockets. In addition to the small surface area that is available for contact with the socket finger, friction during testing results in carbon build up at the contact points of the socket fingers, creating further problems with cross contamination. There is therefore a need to provide a testing socket with Kelvin contacts which can avoid the above-stated pitfalls in practical use.